Discussion. B. sonorus is most closely related to 5. pennsytvanicus, which does not occur in CaliforČnia, and somewhat related to cal\fbrnkm and Jfrr-v&fttt. It can be separated from the latter two in the male by having apices of penis valves longer than wide, and in the female by having black hair on metasomal tergite 4.
Peters (1968) and Milliron (1973a) considered sonorus to be conspecific with pennsylvanlcus. Their evidence is not based on intergradation. RWT has seen specimens of both species from the same localities in southern Texas without signs of inter-gradation. The resolution of this problem awaits further studies in southern Texas and central Mexico where these bees occur together.
We have taken several late season nests, and successfully reared a nest from a confined queen
which was originally produced, mated, and overwin-tered in our lab. Nests are typically located under-ground in abandoned pocket gopher burrows. This species is extremely pugnacious in defense of its nest Brood rearing is typical for the subgenus Fer-vkbbombus (see Hobbs 1966a). Ryckman (1953) recorded Physocephala texana as a parasite of this bee, in southern California, and we confirmed this for the Central Valley.